Signal processing device, magnetic information playback device, and signal processing method

Abstract

The invention provides a signal processing device, including: an extraction section that extracts, from an input digital signal, a decoding target signal at an extraction timing that has been determined as a timing for extracting the decoding target signal; a decoding section that decodes the decoding target signal by estimating, by a maximum likelihood decoding, a candidate for a decoding result of the decoding target signal extracted by the extraction section and detecting a maximum likelihood decoding result; and an adjustment section that adjusts the extraction timing using a likelihood of the candidate for the decoding result estimated by the decoding section.

What is claimed is: 
     
       1. A signal processing device, comprising:
 an extraction section that extracts, from an input digital signal, a decoding target signal at an extraction timing that has been determined as a timing for extracting the decoding target signal; 
 a decoding section that decodes the decoding target signal by estimating, by a maximum likelihood decoding, a candidate for a decoding result of the decoding target signal extracted by the extraction section and by detecting a maximum likelihood decoding result; and 
 an adjustment section that adjusts the extraction timing using a likelihood of the candidate for the decoding result estimated by the decoding section, 
 wherein adjustment of the extraction timing by the adjustment section is initiated on a condition that a predetermined time, which is an upper limit time in which deviations in the extraction timing are permissible, has elapsed from initiation of extraction of the decoding target signal by the extraction section, and 
 wherein the adjustment section calculates the likelihood based on the extracted decoding target signal each time the decoding target signal is extracted by the extraction section, and adjusts the extraction timing using the calculated likelihood each time the likelihood is calculated. 
 
     
     
       2. The signal processing device of  claim 1 , wherein the decoding section comprises:
 a detection section that estimates the candidate by the maximum likelihood decoding and detects the maximum likelihood decoding result; and 
 a correction section that corrects errors in the maximum likelihood decoding result detected by the detection section. 
 
     
     
       3. The signal processing device of  claim 1 , wherein, after the predetermined time has elapsed from initiation of extraction of the decoding target signal by the extraction section, the adjustment section calculates the likelihood based on the extracted decoding target signal each time the decoding target signal is extracted by the extraction section, and adjusts the extraction timing using the calculated likelihood each time the likelihood is calculated. 
     
     
       4. The signal processing device of  claim 3 , wherein, irrespective of whether or not a maximum likelihood decoding result has been detected by the decoding section, the adjustment section calculates the likelihood based on the extracted decoding target signal each time the decoding target signal is extracted by the extraction section, and adjusts the extraction timing using the calculated likelihood each time the likelihood is calculated. 
     
     
       5. The signal processing device of  claim 1 , wherein, the lower the likelihood, the more the adjustment section reduces an adjustment amount of the extraction timing. 
     
     
       6. The signal processing device of  claim 1 , wherein the likelihood is calculated using soft information generated based on the decoding target signal. 
     
     
       7. The signal processing device of  claim 6 , wherein:
 the soft information comprises a maximum likelihood path metric and a competing path metric; 
 the likelihood is defined by a probability that the decoding result is accurately detected by the decoding section; and 
 the probability is calculated using the maximum likelihood path metric and the competing path metric. 
 
     
     
       8. The signal processing device of  claim 7 , wherein the adjustment section adjusts the extraction timing using an adjustment amount τ k−1  that is obtained using the following Equation (1), Equation (2) and Equation (3):
   ε k   =y   k   d   k−1   −y   k−1   d   k   Equation (1):
 
   θ k =θ k−1   +g   k βε k   Equation (2):
 
   τ k+1 =τ k   +g   k αε k +θ k   Equation (3):
 
 wherein, in Equation (1), Equation (2) and Equation (3), k is a natural number; ε is a phase error between the decoding target signal and an ideal decoding target signal; y is a signal level of the decoding target signal; d is a signal level of the ideal decoding target signal; τ is an adjustment amount of the extraction timing; g is the probability; θ is a derivative term of an error in the extraction timing; and α and β are adjustment items. 
 
     
     
       9. The signal processing device of  claim 1 , wherein the maximum likelihood decoding is a maximum likelihood decoding according to a Viterbi algorithm. 
     
     
       10. The signal processing device of  claim 1 , further comprising an amplitude component adjustment section that adjusts an amplitude component of the decoding target signal, wherein the decoding section estimates, by the maximum likelihood decoding, the candidate for the decoding result of the decoding target signal, the amplitude component of which has been adjusted by the amplitude component adjustment section, and detects the maximum likelihood decoding result. 
     
     
       11. A magnetic information playback device, comprising:
 a reading head that reads magnetic information from a magnetic recording medium; 
 a generation section that generates a digital signal from the magnetic information that has been read by the reading head; and 
 the signal processing device of  claim 1 , to which the digital signal generated by the generating section is input. 
 
     
     
       12. The magnetic information playback device of  claim 11 , wherein the magnetic recording medium is a magnetic tape. 
     
     
       13. The magnetic information playback device of  claim 12 , wherein adjustment of the extraction timing by the adjustment section included in the signal processing device is initiated on a condition that a predetermined time, which is a permissible time for jitter that occurs in conjunction with conveyance of the magnetic tape, has elapsed from initiation of extraction of the decoding target signal by the extraction section included in the signal processing device. 
     
     
       14. A signal processing method, comprising:
 extracting, from an input digital signal, a decoding target signal at an extraction timing that has been determined as a timing for extracting the decoding target signal; 
 decoding the decoding target signal by estimating, by a maximum likelihood decoding, a candidate for a decoding result of the extracted decoding target signal and detecting a maximum likelihood decoding result; and 
 adjusting the extraction timing using a likelihood of the estimated candidate for the decoding result, 
 wherein adjusting the extraction timing is initiated on a condition that a predetermined time, which is an upper limit time in which deviations in the extraction timing are permissible, has elapsed from initiation of extraction of the decoding target signal by the extraction section, and 
 wherein the likelihood is calculated based on the extracted decoding target signal each time the decoding target signal is extracted by the extraction section, and extraction timing is adjusted using the calculated likelihood each time the likelihood is calculated.